Separation of pyrite, arsenopyrite, and pyrrhotite by flotation



' Patented Febi22,1944

SEPARATION OF PYRITE, ARSENOPYRITE,

AND PYRRHOTITE BY FLOTATION Earl G. Herkenhofl, Stamford, Conn., assignor to American Cyanamid- Company, New York N. Y a corporation of Maine No Drawing. Application February 2, 1943, Serial No. 474,491

4 Claims.

This invention relates to a process of separating pyrite from arsenopyrite and/or from pyrrhotite by froth flotation.

Many sulfide ores contain mixtures of pyrite and arsenopyrite and in some cases mixtures of pyrite, arsenopyrite and pyrrhotite. It is desirable to obtain concentrates of the minerals separately because of the different uses to which the minerals may be put. Thus, for example, if -pyrite is to be burned to sulfadioxide for the production of sulfuric acid by the contact process the presence of arsenic is undesirable and pyrite containing considerable amounts of arsenopyrite is not suitable for this purpose. The mixed ores may in some cases contain precious metal values, particularly gold or silver, and it is common in such cases for the precious metals to be primarily associated with the arsenopyrite. Inasmuch as the precious metal content of such ores frequently represents a considerable portion of the values it is important to obtain a concentrate which contains a large portion of the arsenopyrite.

It has been proposed in the past to depress one or other of the minerals by the addition of agents such as lime )r sodium cyanide. These procedures do result in some separation but the separation is not sharp and leaves much to be desired.

According to th present invention froth flotation is effected after conditioning with a small amount of a permanganate such as sodium or potassium permanganate. The permanganate depresses the arsenopyrite and pyrrhotite, whereas pyrite is but little affected and can thereafter be recovered as a concentrate by froth flotation. In the case of ores containing onlypyrite and arsenopyrite this procedure results in a. satisfactory practical procem.

It has further been found that the depressing action of the permanganate is not the same for producing a concentrate containing pyrite and arsenopyrite which can then be conditioned with larger amounts of permanganate and again floated to produce a pyrite concentrate.

The amount of permanganate used will, of course, vary with the nature of the ore and with the relative contents of arsenopyrite and pyrrhotite. In general a satisfactory depression of ars'enopyrite is obtainable with amounts of permanganate of the order of a quarter of a pound per ton or less. Selective depression of pyrrhotite without depressing arsenopyrite will ordinarily require amounts of permanganate less than 0.05 pound per ton.

It is an advantage of the present invention that the flotation operation on the conditioned pulp is not-critical and the normal sulfide flotation reagents may be used such as xanthates, dithiophosphates, mercapto-benzothiazoles, and the like. While ordinary sulfide reagents may be used, they differ somewhat in eflfectiveness, and I have found that the best results are obtained with dithiophosphoric acids, dithiophosphates, or mixtures of dithiophosphates with mercaptcbenzothiazole and reagents of this type are preferred.

The invention will be described in greater detail in conjunction with the following specific examples. The parts are by weight.

EXAMPLE 1 An ore containing pyrite, arsenopyrite and pyrrhotite, associated with a gangue which also contained iron and sulfur, was treated for high arsenopyrite recovery. The arsenic content represented the major value or the ore under present economic conditions. The ore was first subjected to a bulk sulfide flotation with stage oiling using dicresyldithiophosphoric acid and sodium iso- V propyl xanthate as promoters. The concentrate was then conditioned with 0.02 lb. ofpotassium permanganate and floated in two stages usin a small. additional amount of the dicresyldithiophosphoric acid. The purpose of the flotation was to produce a nvrite-arsenopyrite concentrate with a maximum rejection of the pyrrhotite. The sequence. of conditioning and amounts of re.-

Conditions and reagents benzothlazole dlsecondarybutyldithiophoshate reagent.

Conditions Reagents, pounds per ton Point at addition Time, minutes NB CO Condition nd. eoneentrate. Cl. flotation I .The promoters are referred to by tradedesig- Metallurgical results nation. "AF is dicresyldithiophosphoric acid diluted withcresols. "343 is sodium'isopropyl 2 Per Assays xantha'te- Product cent gi Metallurgical results Weight is Assays good).--" 1034511: 8.5; Product Weight 26 ii'colfii::::::'"""'::::::::::::::::::::::::: 1:13 18:10 As Fe S 01. Tall. 3.59 0. 37 Rgh.Tail 94.71 0 015 Comb. Cone .i-. 1.70 12.77 Per cent Percent Percent Rgh. Cone 5.29 4.36 1 0.24 15.95 3.28

g '15'653 353 3523 so It illb t th t h h d r w eapparena a 1g egree 0 con- Rgh'Tafl 9M7 M06 centration of arsenopyrite was obtained, 84 to 1,

It will be apparent that a very effective depression of pyrrhotite took place and a major portion of the arsenic was recovered in a relatively high grade arsenopyrlte-pyrite concentrate.

When the same procedure was carried out but the potassium permanganate conditioning omitted the cleaner concentrate contained only 4.56% of arsenic and but little rejection of pyrrhotite took place. EXAMPLE 2 and the pyrite concentration was even higher, amounting to 196 to 1.

A blank test which followed the same sequence but omitted the potassium permanganate conditioning gave an arsenopyrite concentrate having only 1.17% of arsenic, more than 92% of the arsenopyrite remaining in the pyrite concentrate.

Flotation operations in the examples were carried out under standard conditions using Fagergren flotation machines and operating conditions such as air and the like were the same for both.

blank tests and those using permanganate conditioning. b

In the examples potassium permanganate has been described because of its ready availability. sodium permanganate gives the same result and inlarge scale use presents some economies.

I claim:

1. A method of separating pyrite from arsenopyrite which comprises subjecting a mixture containing both to conditioning with a sufliclent alkali metal permanganate to depress the ar'senopyrite and subjecting the conditioned material to froth flotation in the presence of a promoter for Conditions and reagents Conditions n Reagents, pounds per ton Point of additions v 'fgfi f g gg pH cuso. mic 0. AF 15 34s KMn0 P. o 404 3 0- 4.0 g. v 0.111 p 0. 05 i 0. 015 '2 0. 039 10 0. 06 00nd. 01. 00110. 1 0. 054 0.03 Py. flotation 3 0.02 added at 5 minutes.

The promoters are referred to by trade designation. AF 15 is a dicresyldithiophosphoric acid diluted withcresols. 343" is sodium isopropyl xanthate. P. 0. stands for pine oil and pyrite, whereby a concentrate is obtained rich in pyrite and a tailing rich in ars'enopyrite.

2. A method of separating pyrite, arsenopyrite and pyrrhotite which comprises subjecting a mix 404" for an undiluted mixed sodium mercaptoture containing the three minerals to conditioning with a small vamount of an alkali metal permanganate sumcient to depress the pyrrhotite but insuflicient to substantially depress the arsenopyrite, subjecting the conditioned material to froth flotation in the presence of a sulfide propyrite and subjecting the conditioned material to- ,froth flotation in the presence oi a sulfide col- 10 acid radical.

iector whereby a concentrate is produced rich in 1 Pyrite and a tailing containing thearsenopyrlte.

3. A method according .to claim 1 m which the froth flotation takes place in the presence of a collector" containing the dithiophosphoric acid 4. A method according to claim 2 in which both flotation operations are eflected in the presence oi a collector containing the dithiophosphoric EARL c. rmnxnmror'r'. 

